<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>调试工具</title>
</head>
<body>

<script>
function foo() {
  var a = 10;

  function fn2() {
    var b = 10;
    console.log(b);
  }

  function fn1() {
    console.log(a);
  }

  fn2();
  fn1()
}

foo();
</script>
</body>
</html>